(a) The Field of Invention
This invention relates to specialized vehicles known as straddle carriers that are used for such purposes as lifting and manipulating large packing containers and transport van bodies.
(b) Description of the Art
A straddle carrier is a vehicle that can either move over a load or bring a load underneath its structure, so that it can lift the load and carry it about with ground engaging wheels of the carrier being on both sides of the load. They are typically used in the handling of large, standardized shipping containers transported on railway cars and in barges and ships. They are also used in lifting and moving vans of trailer trucks, such as used in "piggyback" shipping. A straddle carrier finds use in loading and unloading containers from a railway car or a ship, or in stacking containers one above another in storage depots, or in trans-shipping containers and vans from one type of conveyance to another.
A typical form of straddle carrier has a central bay defined by side frames and an arched framework bridging between the side frames that extends over the bay. The side frames have ground engaging wheels that are powered and steerable. A cab for a driver is at one end, and in use the straddle carrier is driven over a load, the load is lifted so as to be supported from the arched framework, and the carrier is then driven for transporting the load to its next location. In such straddle carriers the carrier itself is driven about to move the load from one location to another.
There are similar forms of cargo handling apparatus which also raise, lower and straddle loads. These commonly comprise overhead cranes supported on wheel mounted frameworks to have a mobile apparatus. Typical of these structures are rail mounted cranes that travel alongside piers and docks in shipyards and ports. They usually employ either luffing or overhead traveling cranes that overhang the ships they service, and in some of these structures the crane can travel inside the wheel mounted framework in order to carry loads along a pier or docks from one point to another.
The art has not provided highly mobile container handling machines that are sufficiently versatile to function in a confined space to straddle a load, shift the direction of alignment of the load while standing still, support the load either within the perimeter of its ground engaging supporting structure or in a position cantilevered from such structure, and also turn within a short radius to achieve mobility. A straddle carrier having these several attributes would be particularly useful in railroad yards for trans-shipping containers or semi-trailer vans between railroad cars and trucks. If an ordinary straddle carrier is to be driven over a line of railcars to load or unload them, it has to be driven over the line of cars for each successive pick-up or depositing of a container. Also, aisle space is required on each side of the railcars to accommodate the straddle carrier. In addition, aisles between railroad tracks are narrow and frequently crowded with freight and machinery. Thus, the use of ordinary straddle carriers having load carrying bays between opposing side frames is not satisfactory for loading or unloading a string of railcars.
Four wheeled straddle carriers, with ground engaging wheels at the four corners of a rectangular base area, cannot easily be manipulated within the confines of aisles in railway yards. The turning radius of a four wheeled vehicle is relatively large, and alongside most rail tracks there is not sufficient room to turn and maneuver a four wheeled straddle carrier. There has, therefore, been a need for a mobile load handling machine that can efficiently serve confined areas, where it is not possible to simply drive a stradle carrier over the load and then drive away with the load.